Patrons of the bustling Brooklyn Heights branch said they felt baked thanks to a faulty air-conditioning system that hasn’t worked all summer long and, according to library honchos, won’t be replaced until next summer.

“It truly feels like an oven in here,” said Diane Graglia, 69, of Brooklyn Heights. “I used to go all the time to read and socialize, but it’s like a million degrees inside now and just too unbearable.”

Around 2 p.m. yesterday, temperatures on the second floor of the Cadman Plaza West building – one of the borough’s busiest library branches – slightly topped a toasty 100 degrees, according to thermometer readings conducted by a Post reporter.

By 2:30 p.m., librarians drenched in sweat closed off the second floor, limiting visitors to the ground floor’s business library where temperatures were slightly more bearable — 96 degrees. Fans blowing hot air offered little relief as did open windows.

By 4 p.m., with indoor temperatures still hovering near 100 degrees, Brooklyn Public Library officials closed the entire branch four hours early as a safety measure.

“It was terrible,” said Alison Wildman of Prospect-Lefferts Gardens, who left the library within minutes upon arrival with her 8-year-old son, Jelani Robert. “I wanted to take him to the children’s section, but I just couldn’t take the heat.”

The branch will remain closed today as outdoor temperatures are expected to reach up to 96 degrees, officials said.

It will mark the eighth time since June 22 that the branch was closed due to excessive heat.

Jason Carey, a Brooklyn Public Library spokesman, said the five-decade-old branch’s air conditioning system “is very old and beyond repair.”

The system has been on the fritz for years but broke down for good two weeks ago, he added.

In early July, four other borough libraries also shut down for a few days due to faulty air-conditioning systems. But the others have since been fixed or compensated for with temporary systems.

Carey said BPL is “considering” setting up a temporary air-conditioning system at the Brooklyn Heights branch similar to one recently set up at the Fort Greene branch.

Meanwhile, a Queens man is believed to be the city’s first heat-related death this summer. James Edwards, 71, was found collapsed in his apartment in Corona yesterday. An autopsy will determine the cause of death.